Berkeley DB Family

Nope, no dirty reads in Oracle.

No blocking in Oracle either.

But, ahem, your snapshot might get a bit too old.

The Oracle Db allows :
1) readers of the data not to be blocked by writers of the data
2) writers of the data not to be blocked by readers of the data

You can find info reading the following...
http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/consist.htm#insertedID3

Greetings...
Sim

That's one of my favourite topics.
In oracle select doesn't block anything except when we want it to. And Oracle the isolation level read committed is preserved by default that means as mentioned by Sim, in oracle, Readers don't wait for writes and writers don't wait for readers.
Please read the link that is mentioned by Sim.And just a suggestion, if you are in Oracle world, think from oracle point of view. I meet lot of people every week who wants x feature implemented in database abc in Oracle.Well it may be there , may not be.
Have fun with Oracle.
Aman....

Yes... exactly these characteristics permit Oracle DB to be the more scalable DB in the world....

Greetings...
Sim

100% and also no lock escalation as like other db's.
Aman....

yes, we all know that Oracle has unlockable read from rollback segments using SCN, but as DBA I WANT to see uncommited data of some of my hanged applications to know what they are doing before they commit.

And how can I do it?

You may want to read:

http://laurentschneider.com/wordpress/2008/08/read-uncommitted.html

Not helpful...
If I had a chance to interfere with first session and suspend transaction in it, I also could see it's data in it. But as I stated above, session is hanged in application server and I need to see its data. Looks like Oracle dont bother such administrative monitoring things.

Actually, the link was to support that you won't be able to do so.....

The last line in the link: 'But no, the SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED is not supported in Oracle

'

You are right. Oracle does not bother with such things, as they are rarely needed in Oracle in a well designed application.

Unfortunately many developers are not aware of things like DBMS_APPLICATION_INFO which would help weird monitor situations.

You can see SQL involved by starting with code example below

  1  SELECT USERNAME, ss.sql_text
  2  FROM   v$session vv, v$sql ss
  3  WHERE  vv.TADDR IS NOT NULL
  4*  and   vv.prev_sql_id = ss.sql_id
SQL> /

USERNAME
------------------------------
SQL_TEXT
--------------------------------------------------------------------------------
DBADMIN
insert into ora4063 values (1,2)

I issued the INSERT in a different terminal window & did not COMMIT;

Hi Claire,

In addition to everyone else's comments, I would add this:

It's important to understand that when you come from a different database system, such as SQL Server, for example, that concepts may not map in a 1 to 1 manner. It's better to ask about the problem you're trying to solve, rather than ask "How do I do this particular task in Oracle?" Problems in Oracle may map to a completely different set of tasks than in SQL Server.

If you had started out by asking "How can I monitor in-process, uncommitted data, in order to understand what's happening with my application when it gets hung?", you may have gotten a pointer to DBMS_APPLICATION_INFO, or DBMS_PIPE or UTL_FILE much more quickly.

Hope that helps,

-Mark